The technical field generally relates to aftertreatment control of emissions in internal combustion engines, and more specifically but not exclusively relates to design and modeling of aftertreatment catalytic systems.
Selective catalytic reduction (SCR) systems depend upon the injection of ammonia or urea, or sometimes an alternate reductant such as hydrocarbons, into the system. The injected reductant processes in the exhaust gas, ultimately entering the gas phase and adsorbing to the catalyst surface for reaction with adsorbed NOx from the engine. The reductant may have to experience evaporation, hydrolysis or other decomposition, and adsorption. The resulting exhaust gas composition can be variable across the exhaust system cross-section, resulting in variability in available reductant and in the ratio of reductant to NOx or other reactants.
SCR systems, and other aftertreatment systems, for mobile applications such as vehicles are highly sensitive to cost and packaging footprint. Catalyst sizing therefore is closely matched to capability, with the smallest catalyst having the lowest catalyst loadings that will meet the needs of the application being utilized. The needs of the application include accounting for part to part variability in manufacturing, degradation over time and events such as high temperature excursions or exposure to sulfur. The uniformity profile of injected and processed reductant is a part of the performance of the aftertreatment system, and designs having lower uniformity ultimately require relatively larger catalysts and/or catalyst loadings to meet the requirements of the application.
The determination of the uniformity is a challenging operation, and can require a large amount of design effort and numerous design iterations. Analytical solutions, such as computational fluid dynamics (CFD) operations allow multiple systems to be tested and adjusted more cheaply, but do not always match real systems. Presently known testing rigs for determining uniformity of exhaust gas constituents, and accordingly for calibrating a CFD design and/or for testing a physical design, require significant warm-up and preparation periods, allowing for only a few data point acquisitions each day. Therefore, further technological developments are desirable in this area.